DR9303-CS 960207 WIER & A- SOI::IATES, INC.
ENGiNE:F'RiNE~ SURVEYINr= IA. ND PLANNIN(3
4300 BELTWAY PLACE SUiTE 130 * ARLINGTON, TEXAS 76018
METRO 817/467-7700 · FAX 8171465-7482
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IO'd 88PL 99~ LIS 'ON X~H SH£VlOOSS¥ ~ ~IH~ ~ 9I:80 flHL 96-LO-HHH
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Engineering, Surveying & Land Planning
3g08 South Freeway
FT. WORTH, TEXAS 76! ! 0
(817) 926.7774
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Engineering, Surveying & Land Planning
3908 South Freeway
FT WORTH, TEXAS 76110
(g17) 926-7774
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fo! box cuivell, Figures Ic) or 20 fo! circular
pLpe, Figure 26 for elliptical pipe, and Figure 31
for pipe-alch- Outlet vehicity is based on design
~ischar~ and full flow at the outlel. S~p lo step
17.
11. If ~ ~ g~eatc~ Ih~ eritic~ depth dc, skip to
step 13. otherwise;
12. Calculate HW by Type I o~nt~n p~ocedutc
~=dc+ Vc2[2g+ he +hr-SoL -
13.
Outlet velocity equals critical velocity Vc- Skip
to step 15.
if TW is ~ealer than D, the outlet is ~ubmerged
and the culvert is on a mild slope, go to step 10,
olherwise;
F Type 1] operation procedure.
2 L
HW = TW + YTW /2g + he* hr- So
15.
17.
vided by the area of Bow at tailwater depth.
If HW is less than t.2D, skip to stap 17,
otherwise;
The check should be made here for operation
Type IV B. At this petal, it has been determined
thatSo< Sc. TW< D, andlTW ~> 1.2Dby
calculation frmn Type ] or Type II. Calculate a
new HW based on HW -- H + P- SoL H is
clctesmined f~om a n~moglaph on Figure 12 for
box culverts, Figures 19 or 20 for ckcular pipes,
Figmc 26 for el}SpliCe[ pipes, and Figure 31 for
pip,.arch, P is ~qual lo (dc * D)/'2 if TW is less
than dc and P is equal to TW if TW is g~eater
than dc. ~ is an appruXinmtion of the hydraulic
grade line. Calculate oulint velocity baaed on dc
if TW ii less Iban dc and baaed on TW if TW is
IFealer than dc.
At thin point, an HW and outlet ~elocity ha~
been caisulased ('or tile design discharge passage
through a trial size culvert. )f the calculated HW
is less than or equal to the allowable headwater
HWA and. in addition, the calculated HW is not
appreciably lower than HWA (an indication of
increased (by adding barrels, widening spans,
increasing diameter, cie,). Also, Ihe culvert slope
might bc adjusted slightly to came a reduction in
HW. Regardleae of the charters made. the calcu-
lations must be redone; ~o back to Step 3. If the
calculated HW is considerably lower than I-IWA
or lower than the ct~lvert depth D, in ord~ to
find a more economical stmelure, the trial
culvert size should be reduced, by reducing the
number of barrels, reducing span widths, se-
ducing diameter, etc. Thc calculatior$ must then
be redone after any changes; ~o back to step 3.
*A good nleasure of this is to compare the HW
with thc culvert depth D. If HW is below ID, the
efficiency of that colvett size is olr6ously not
very high.
18. The culvert for which lhe calculated HW is
satisfactory may ha~ an excursive outlet veloc-
ity. }ual what outlel velocity is 'excessive' is
normally an angineeling judgement based on
local conditions. It is usually always most eco-
nomical to provide tiptop, or sills, or a slilllng
basin or ~he like at thc outlet and to contra[ any
excessive velocity. (Sec Velocity Control De-
vices. Section 4.-702) Generally, a p~operb/sized
culvert will have an oullet vebcity greater than
the natural stream velocity. Any oullct velocity
control device is considered par of the hydraulic
design el the culvert.
19. If the culvert is operating on entranCe controlas
found in Type IIIA m' ]liB, the possibility exists
of improvin~ the entrance conditions so as to
reqinse a less costly structure. This is done by
investigating tile design of a flared (or tapered)
inlet and aSSOciated structure. The design proce-
dures are discussed in Section 4-603 for pipe
culverte and at Section 4-604 [o1' box culverts.
Due to the goat of Ihe improved entrance, an
economic comparison should be made between
the ~i~ with a normal entrance and the design
with an improved entrance. Go to step 18 after
the improved entrance design is complete,
4-603. IMPROVED INLET D£SIGN - FIEF.
For pipe culverts bn slopes GREATER THAN CRIT-
ICAL SLOPE.
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